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• avformat/matroskadec : factor the prores packet parsing code out

  4 avril 2018, par James Almer

  avformat/matroskadec : factor the prores packet parsing code out
  Simplifies code in matroska_parse_frame(). This is in preparation for
  
  the following patch.
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libavformat/matroskadec.c

• Stretch Subtitles Timing by Factor

  3 août 2022, par Matt McManis

  I'm muxing an mkv video, but the Subtitle .ssa file is out of sync by around 1 second by the end of the video.

  



  Delaying the subtitles by 1 second in the beginning is not enough, the timing needs to be stretched to fix an exponentially growing delay. Sync starts out fine in the beginning, but a few milliseconds delay multiplies for each minute that passes.

  



  I fixed them using MKVToolNix with Stretch 0.999.

  



  ---

  



  How can I stretch Subtitles using FFmpeg ?

  



  I saw here how to stretch audio by a factor the same way. ffmpeg, stretch audio to x seconds

  



  I'm using something like this :

  



  ffmpeg -y 

-fflags +genpts 

-i "video.m4v"  
-i "audio.ac3" 
-i "subs.ssa" 

-c:v copy 
-c:a copy 
-c:s copy 

-map 0:v? 
-map 1:a? 
-map 2:s?

"video.mkv"


  



  I used -itsoffset -00:00:01.000 to remove a gap in the beginning, but it does not stretch.

  


• Eliminate slow speed factor in ffmpeg and image-magic commands

  24 octobre 2018, par Junaid Farooq

  The basic idea of these commands is to create a compare, (A compare has defined a jpeg from past and one from the present, combine such as they will slide on each other and show before after images.)

  e.g. https://media.evercam.io/v1/cameras/1lowe-scnoe/compares/lower-jreyh.gif

  All the commands are written below, doing these operations

  • Resize before after image.
  • create a Gif using both images.
  • Add a log to Gif.
  • Create an MP4 file of from GIF.
  • Create a thumbnail from mp4 file.

  the logo is :

  

  we are making animation and mp4 files using FFmpeg and ImageMagick commands such as

  ffmpeg -i before_image.jpg -s 1280x720 before_image_resize.jpg
  
  
  
  ffmpeg -i after_image.jpg -s 1280x720 after_image_resize.jpg

  The above commands are first to resize both images which are going to be used in animation.

  This command is being used for creating a gif.

  convert after_image_resize.jpg before_image_resize.jpg -write mpr:stack -delete 0--1 mpr:stack'[1]' \\( mpr:stack'[0]' -set delay 25 -crop 15x0 -reverse \\) mpr:stack'[0]' \\( mpr:stack'[1]' -set delay 27 -crop 15x0 \\) -set delay 2 -loop 0 temp.gif

  This command to add a logo to the animation.

  convert temp.gif -gravity SouthEast -geometry +15+15 null: evercam-logo.png -layers Composite compa-efxfphu.gif

  Then to create an mp4 file as

  ffmpeg -f gif -i compa-efxfphu.gif -pix_fmt yuv420p -c:v h264_nvenc -movflags +faststart -filter:v crop='floor(in_w/2)*2:floor(in_h/2)*2' compa-efxfphu.mp4

  then to create a thumbnail from this mp4.

  ffmpeg -i compa-efxfphu.mp4 -vframes 1 -vf scale=640:-1 -y thumb-compa-efxfphu.jpg

  Is there any possibility to reduce any of these steps ? This all takes a lot of time, I am merely interested in both convert commands, can we make them into one command ?

  Or do you see any chance to reduce these all 4 in one ? any input will be so thankful.